The chip plane equipped with component structures can have coefficients of thermal expansion α1, α2 differing from one another in different directions, depending on the crystal axes. This is particularly the case for surface acoustic wave chips with a piezoelectric substrate whose physical properties exhibit anisotropy. The coefficients of thermal expansion α1, α2, are generally larger than the coefficient of thermal expansion αp of the underlying carrier substrate. In case of a change in temperature, the change in length of the chip is greater than that of the carrier substrate.
The chip is mechanically fixed to the carrier substrate by means of solder joints (bumps). These solder joints are therefore subject to mechanical stresses that arise due to the difference Δα1=|αp−α1| and Δα2=|αp−α2| in the coefficients of thermal expansion of the chip and the carrier substrate. In case of differing coefficients of thermal expansion of the chip and the carrier substrate, the outermost bumps and the carrier substrate, in particular, are subject to the strongest stresses form the shearing force F(F1, F2) acting on them. F1 is the force component in the first preferred direction x1. F2 is the force component in the second preferred direction x2.